Many different types of data storage systems exist and are being used to store data cartridges at known locations and to retrieve those data cartridges from the storage locations so that data may be written to or read from those data cartridges.
A typical data storage system may include one or more cartridge receiving devices for holding the various data cartridges. For example, one type of cartridge receiving device may comprise a cartridge storage rack or “magazine” while another type of cartridge receiving device may comprise a cartridge read/write device. Cartridge read/write devices come in various sizes including full-width cartridge read/write devices and, more recently, half-width cartridge read/write devices.
The data storage system may also be provided with a cartridge access device for accessing the various data cartridges contained in the various cartridge receiving devices. The data storage system may also include a cartridge positioning system that is operatively associated with the cartridge access device. The cartridge positioning system is used to move the cartridge access device among the various cartridge receiving devices, thereby allowing the cartridge access device to access the data cartridges that may be contained in the various cartridge access devices. Typically, when certain data contained on a particular data cartridge are desired, a host computer system will issue a command to a control system associated with the data storage system. The control system then actuates the cartridge positioning system which moves the cartridge access device along the cartridge storage magazines until the cartridge access device is positioned adjacent the desired data cartridge. The cartridge access device then removes the data cartridge from the cartridge storage magazine and carries it to the cartridge read/write device. Thereafter, cartridge access device inserts the selected data cartridge into the cartridge read/write device so that the host computer may read data from or write data to the selected data cartridge. After the read/write operation is complete, the cartridge access device may remove the data cartridge from the cartridge read/write device and return it to its appropriate location in the cartridge storage magazine.
While data storage systems of the type described above work well and are currently being used, the continuing need to store ever increasing numbers of data cartridges can place significant limitations on the data storage system. For example, in data storage systems of the type described above, the data cartridges may be stored in one or more vertical columns or stacks which define a single cartridge access plane. While the data storage capacity of such a system may be increased by increasing the number of data cartridges stored in the vertical columns, there is a limit to the number of data cartridges that can be stored in a given column. That is, the higher the column (i.e., the more data cartridges that are stored in the column), the longer it takes the cartridge access device to access a given data cartridge, particularly if the data cartridge is located at the extreme ends of the column. While more columns of shorter heights may be provided, this comes at the expense and difficulty of providing a positioning system capable of moving the cartridge access device vertically along a given column or stack as well as horizontally along the various rows of storage columns. Regardless of which approach is employed, increasing the data cartridge storage capacity comes at the cost of increasing the overall size of the data storage system thus creating a tradeoff between minimizing size and maximizing storage capacity.
Another design criterion for data storage systems is conserving and minimizing volumetric space. Often, if not always, the more volumetric space that is needed to store data cartridges, the more costly the data storage system. An equally important design criterion is minimizing the time needed for the cartridge access device to access a given data cartridge.
Partly in an effort to increase data cartridge storage capacity, data storage systems have been developed that store the data cartridges in two separate stacks or columns that define two separate cartridge access planes. For example, the data cartridges may be arranged in a pair of columns positioned on opposite sides of the cartridge access device. If this arrangement is used, however, it is necessary to provide the cartridge access device with a “pass-through” cartridge engaging assembly or “picker” that is capable of accessing the data cartridges stored in the two separate stacks. Alternatively, such systems have been provided with “flipping” or rotating picker systems to access the data cartridges stored in both stacks. While this “multi-plane” data storage system is currently being used, the pass-through, flipping, or rotating picker assemblies required for the cartridge access device are relatively complex, expensive to manufacture and tend to suffer from decreased reliability, primarily as a result of the relatively complex mechanical systems associated with such picker assemblies.
Another type of data storage system achieves increased storage capacity by arranging the data cartridges on a rotating magazine stack. While the rotating magazine stack usually does away with the need to provide the cartridge access device with a pass-through, flipping, or rotating picker, the mechanical complexity of the rotating magazine rack, like the picker assembly in the aforementioned “multi-plane” data storage systems, increases manufacturing costs and tends to suffer from decreased reliability.
Consequently, a need remains for a data storage system having an increased cartridge storage capacity that does not require adding any additional volumetric space to the data storage system. Ideally, the data storage system would provide this additional cartridge storage capacity without increasing the overall complexity of the data storage system (i.e., the addition of a pass-through, flipping or rotating picker assembly or a rotating cartridge magazine rack) and without increasing the time needed for the cartridge access device to access the data cartridges.